Are pi bonds stronger than sigma bonds?
1 Answer
No, sigma bonds are stronger than pi bonds because the bonding pair of electrons is localised, on average, closer to the nuclei of the bonded atoms.
The covalent bond is an electrostatic attraction between the positively-charged nuclei of the bonded atoms and the negatively-charged binding pair of electrons in their σ−orbital. Electrostatic attractions are short-range forces and their strength depends on the distance between the opposite charges.
By comparison, a π− orbital formed by the sideways overlap of two p-orbitals locates the electrons rather further away from the bonded nuclei so their electrostatic attraction for the nuclei is a little weaker. The is why the average bond enthalpy for a C=C bond is not quite twice the bond enthalpy of a C-C bond.
